VARIABILITY IN E. COLI AND TRYPTOPHAN-LIKE FLUORESCENCE IN TWO KARST BASINS, INNER BLUEGRASS REGION, KENTUCKY

Karst aquifers are prone to contamination by fecal pathogens, which can enter the subsurface via leaking or overflowing sanitary sewers, failing septic systems, wastewater discharge, and agricultural and urban runoff. Challenges in addressing contamination by pathogens include early detection of their presence. E. coli bacteria are typically used to assess water quality with respect to enteric pathogens, but these simple fecal indicators require culturing and incubation prior to enumeration. A promising alternative is dissolved organic matter (DOM), notably tryptophan-like fluorescence (TLF), which has been positively correlated with E. coli counts in multiple studies and can be monitored with real-time sensors. However, few studies of TLF have been conducted in karst systems or in the USA.

We are examining the utility of TLF monitoring for the Cane Run/Royal Spring (CR/RS) basin in Fayette and Scott counties and the Camden Creek basin in Woodford County in central Kentucky. These karst basins encompass urban (CR/RS) and agricultural (both basins) land uses. Royal Spring and Camden Creek have been sampled and subsequently analyzed for E. coli and DOM weekly since June 9, 2021. TLF has been monitored at 15-minute intervals via a submerged fluorometer at Royal Spring since August 4, 2021, and a similar fluorometer will be deployed at Camden Creek. Preliminary results show similar E. coli concentration ranges at both sites (<10 to 3873 MPN / 100 mL at Royal Spring; 201 to 3255 MPN / 100 mL at Camden Creek). TLF concentrations ranged from <1 to 222 ppb at Royal Spring. Both E. coli and TLF show overall declining trends from summer through fall, with concentrations peaking over periods of hours following storms. TLF is significantly correlated to E. coli for grab samples (r2 = 0.74, p = 0.000005, n = 18). Pending analyses will provide additional information about correlations between DOM components and E. coli concentrations at both sites.